Sticky issue. The original, working style aussie was much different than the big fluffy show aussies you see now, and much closer to the so-called mini aussies. You can still find a working line aussie that weighs under 30 lbs.
Aussie from the 1950's:
What the Australian Shepherd Club of America says:
Those who oppose the promotion of Miniatures feel that breeding a smaller size is unnecessary when a smaller dog can be found among the general population. They are concerned that the act of breeding selectively for size comes at the possible expense of health and structure. The final concern is that by breeding smaller dogs, the Mini breeders are targeting urban pet owners who have little space (small yards, apartment dwellers) and misrepresenting the true nature of a herding dog.
The Australian Shepherd Club of America (ASCA) has taken the position that they do not wish to recognize distinct variations in sizes because there is already an accomodation for that in their breed standard. ASCA will not allow the registration of any dog who is also registered under another breed name or size variation. Naturally, there is the occasional unethical breeder who attempts to ride both sides of the fence by intermingling modern Australian Shepherd lines with Miniature Australian Shepherd bloodlines. This behavior only adds fuel to the arguement that there is no need for a size variations under a different name and those breeders who are caught registering their dogs with both ASCA and a Mini registry are subject to having their registry rights suspended if caught.
My opinion.. the Mini aussie people can't have their cake and eat it too.. they should start establishing their own, unique breed.
The toy aussie is a scam, however, and as soon as you start breeding for dwarfism you add a whole slew of health issues and you no longer have anything resembling a herding dog.
Here's another very informative post:
http://tinyurl.com/qwbhn